A Bayesian analysis of the 69 highest energy cosmic rays detected by the Pierre Auger Observatory

TL;DR

This paper uses Bayesian methods to analyze 69 ultra-high energy cosmic rays from the Pierre Auger Observatory, assessing their likely sources among known active galactic nuclei and galaxy samples, and finds evidence against a purely isotropic origin.

Contribution

It introduces a multi-level Bayesian model to estimate the fraction of cosmic rays originating from specific astrophysical source catalogs, providing a novel statistical approach in UHECR source identification.

Findings

Bayes factors disfavour purely isotropic models.

Estimated source fractions range from 0.08 to 0.25 across catalogs.

Provides credible intervals for source contributions.

Abstract

The origins of ultra-high energy cosmic rays (UHECRs) remain an open question. Several attempts have been made to cross-correlate the arrival directions of the UHECRs with catalogs of potential sources, but no definite conclusion has been reached. We report a Bayesian analysis of the 69 events from the Pierre Auger Observatory (PAO), that aims to determine the fraction of the UHECRs that originate from known AGNs in the Veron-Cety & Veron (VCV) catalog, as well as AGNs detected with the Swift Burst Alert Telescope (Swift-BAT), galaxies from the 2MASS Redshift Survey (2MRS), and an additional volume-limited sample of 17 nearby AGNs. The study makes use of a multi-level Bayesian model of UHECR injection, propagation and detection. We find that for reasonable ranges of prior parameters, the Bayes factors disfavour a purely isotropic model. For fiducial values of the model parameters, we report 68% credible intervals for the fraction of source originating UHECRs of 0.09+0.05-0.04, 0.25+0.09-0.08, 0.24+0.12-0.10, and 0.08+0.04-0.03 for the VCV, Swift-BAT and 2MRS catalogs, and the sample of 17 AGNs, respectively.